Overactive bladder (OAB), a type of pelvic floor disorder, is a symptom complex that is characterized by urinary urgency, with or without urgency-associated urinary incontinence. OAB is often associated with urinary frequency and nocturia in the absence of infection or other obvious pathology.
Current treatment options for OAB include behavioral therapy, pharmacotherapy, and neuromodulation. Behavioral therapies include lifestyle changes, bladder training, and pelvic floor muscle training. Pharmacological agents approved for use in OAB include anticholinergics, beta3-receptor agonists and detrusor injections of neuromuscular blockers. Anticholinergics inhibit the binding of acetylcholine to the muscarinic receptors in the detrusor muscle, thereby suppressing involuntary bladder contractions. This results in an increase in bladder volume voided and a decrease in micturition frequency, sensation of urgency, and the number of urge incontinence episodes. Beta3 adrenergic agonists elicit a direct inhibition of afferent nerve firing independent of the relaxing effects on bladder smooth muscle. Detrusor injections of botulinum neurotoxin type A, a neuromuscular blocker, may be considered for adults with OAB who cannot use or do not adequately respond to anticholinergic medication.
In terms of neuromodulation, the two most commonly utilized techniques are sacral nerve stimulation (SNS) and percutaneous tibial nerve stimulation (PTNS). SNS provides continuous stimulation of the sacral nerve through surgical implantation of a permanent electrode and a permanent pulse generator while PTNS uses intermittent stimulation of the tibial nerve at the ankle with no permanently implanted lead or stimulator. SNS procedures involve making a midline sacral incision and carrying the incision down to the level of the lumbodorsal fascia, which is opened sharply from the midline. The underlying paravertebral muscles are separated or divided, and the sacral periosteum is identified. An electrical lead is ultimately inserted through the appropriate sacral foramen to lie adjacent to the sacral nerve and the lead is sutured to the periosteum to prevent lead migration. An example of PTNS involves percutaneously inserting a fine-gauge needle just above the ankle next to the tibial nerve and placing a surface electrode on the foot. The needle and electrode are connected to a low-voltage stimulator that delivers stimulation pulses to the tibial nerve. PTNS therapy is provided in an outpatient clinic setting and, in general, is performed initially for 30 minutes weekly for 12 weeks, followed by occasional treatments as needed based on patient symptoms. An advantage of SNS and PTNS is that the electrode is placed close to the target nerve providing direct stimulation of the nerve and requiring less energy consumption.
Recent studies have also been carried out regarding the efficacy of transcutaneous tibial nerve stimulation with the use of external electrodes. Electrodes are applied near to the ankle where the tibial/sural nerve is located. It is believed that the electrical stimulation can penetrate the skin delivering tibial nerve stimulation in the same way as PTNS, but without the need for a needle electrode. Transcutaneous tibial nerve stimulation is completely non-invasive, with surface electrodes connected to a battery operated stimulator and applied to an appropriate site of the body. Such treatment generally does not require regular patient visits at clinics and usually is self-administered at home, which is convenient for the patient.